1. Field of the Invention
This invention is related to the synthesis of a cycloaliphatic resin containing silanes with epoxy and alcoxy-silanol functionalities; and its application in coating's formulations, particularly those that are weatherproof
2. Description of the Related Art
Epoxy resins are well known for their excellent chemical resistance, adherence and hardness properties, so they are used in the paint and coatings industry mainly as primers for new constructions or maintenance. It is also known that epoxy resins, mainly those made of epichlorohydrin and bisphenol A, change the gloss in gloss coatings when they are exposed to sunlight, the coatings turn yellow by oxidation of the double bond of the bisphenol molecule resulting in a surface degradation phenomenon known as “chalking”; so they are rarely use as exterior coatings.
The advance in the state of the art of epoxy resins production has allowed the availability of hydrogenated epoxy-cycloaliphatic resins in recent years, which present high sunlight degradation resistance, however their reactivity with the amine hardener is substantially lower than conventional aromatic resins. There are also a large number of silanes with epoxy functionality that perform in a similar way to epoxy-cycloaliphatic resins providing chemical resistance properties, smoothness and flexibility of the epoxy resins and a weather stability comparable to that of silanes.
Polysiloxane resins are used for high temperature resistance coatings, which form very hard but very brittle films with poor decorative properties, besides being much more expensive than epoxy or alkyd resins used in decorative and industrial maintenance. With these contrasting features, both types of resins are not good enough to be incorporated in an ideal coating that meets the high performance requirements of hardness, smoothness, gloss and strength desired in the coatings industry; recent developments have found that both types of contrasting resins complement each other when combined in suitable amount and type, forming hybrid epoxy-polysiloxane resins.
U.S. Pat. No. 4,250,074 (Raymond E. Foscante et al. granted in 1981) discloses a hybridization procedure wherein epoxy and silane polymers are mixed, both finish their polymerization reacting simultaneously, the epoxy polymer reacts with a difunctional amine and the polysiloxane reacts internally through hydrolytic polycondensation. The hybrid polymer is an interpenetrating polymer network (IPN) which forms a film resistant to UV radiation without chalking and has good gloss retention, but the film is brittle and has low impact and abrasion resistance.
U.S. Pat. No. 5,618,860 (Norman R. Mowrer et al. granted in 1997) discloses the use of epoxy cycloaliphatic resins mixed with hydrolyzed silanes which are reacted with an amino-silane hardener and an appropriate organometallic catalyst. The hybrid polymer produces a film with superior hardness and weather resistance compared to a pure epoxy film, however the problems of rigidity, lack of flexibility and impact resistance are still present due to the continuous reactivity of the remaining radicals.
In later inventions, such as the U.S. Patent application No. 2007/0213492 (Norman R. Mowrer et al., published on Sep. 13, 2007) (PPG), cycloaliphatic resins are also used in hybridization with silane intermediates, such as methoxy-functional DC-3074 from Dow. Other examples include silanol functionalized resins such as DC-840 and Z6018 also from Dow Corning, that also end up in hydrolytic polycondensation aided by previous hydrolysis of the methoxy radicals from the intermediates and by water coming from atmospheric humidity. In this latest development, the silane intermediates necessarily require intermixing with hydrogenated epoxy resins or silanes with epoxy functionality.
The need to protect stone, metal, wood, plastic, cement and others substrates is permanent. This requires the use of coatings having very good impact resistance, toughness, weatherability and gloss retention and that allow hybridization with either epoxy or other resins such as acrylic, polyester or polysiloxane to achieve specific characteristics of performance and cost.